Question

我正在编写一个查询来使用全文搜索来搜索mysql表：

select title, 
  MATCH(title,sidebarTxt,introTxt,fullTxt) AGAINST ('MY KEYWORDS' IN NATURAL LANGUAGE MODE) AS score 
from tbl_news
where (status='published') 
order by score DESC

以上查询工作正常。但是，如果我尝试在where子句中使用'score'，MySql会在'where子句'中抛出错误“＃1054 - 未知列'得分'。以下代码无效：

select title, 
  MATCH(title,sidebarTxt,introTxt,fullTxt) AGAINST ('MY KEYWORDS' IN NATURAL LANGUAGE MODE) AS score 
from tbl_news
where status='published' and score > 0 
order by score DESC

如果你能帮助我理解它，我将非常感激。

Answer 1

如果score是计算列，则无法在WHERE子句中使用score。您必须在其他HAVING子句中设置它以在计算后应用条件：

SELECT title, MATCH(title,sidebarTxt,introTxt,fullTxt) AGAINST ('MY KEYWORDS' IN NATURAL LANGUAGE MODE) AS score FROM tbl_news WHERE status='published' HAVING score > 0 ORDER BY score DESC;

测试用例（使用不同的表）。此处host是一列，host2是派生列。当然，列的推导和选择是假的，没什么意义：

mysql> use mysql; Database changed mysql> select host, UPPER(host) as host2 FROM user WHERE host = 'nottingham'; +------------+------------+ | host | host2 | +------------+------------+ | nottingham | NOTTINGHAM | +------------+------------+ 1 row in set (0.00 sec) mysql> select host, UPPER(host) as host2 FROM user WHERE host = 'nottingham' AND host2 = 'NOTTINGHAM'; ERROR 1054 (42S22): Unknown column 'host2' in 'where clause' mysql> select host, UPPER(host) as 'host2' FROM user WHERE host = 'nottingham' AND host2 = 'NOTTINGHAM'; ERROR 1054 (42S22): Unknown column 'host2' in 'where clause' mysql> select host, UPPER(host) as `host2` FROM user WHERE host = 'nottingham' AND host2 = 'NOTTINGHAM'; ERROR 1054 (42S22): Unknown column 'host2' in 'where clause' mysql> select host, UPPER(host) as host2 FROM user WHERE host = 'nottingham' HAVING host2 = 'NOTTINGHAM'; +------------+------------+ | host | host2 | +------------+------------+ | nottingham | NOTTINGHAM | +------------+------------+ 1 row in set (0.00 sec)

Answer 2

问题是在查询完成运行之前，所有行都不知道score值。因此，无法使用score子句在WHERE上应用条件。在计算完所有结果行之后执行ORDER BY，因此使用它没有问题。

尝试使用HAVING：

SELECT title, MATCH(title,sidebarTxt,introTxt,fullTxt) AGAINST ('MY KEYWORDS' IN NATURAL LANGUAGE MODE) AS score
FROM tbl_news
WHERE status='published'
HAVING score > 0
ORDER BY score DESC

HAVING子句的行为几乎与WHERE一样，差异是>在计算结果行之后执行。此时，每个结果行都知道score的值，并且可以应用条件。

文档：
Fulltext search：查看示例，他们使用HAVING
Syntax of SELECT：查看有关HAVING用法
的部分

Answer 3

编辑：错误

尝试将单引号添加到：as 'score' ...它似乎无法识别您指定该列的名称。

Answer 4

这很可能是50％噪音的情况。当你有一个50％或更多行的单词时，mysql认为它是一个 noise 单词，并在得分（因此排名）时忽略它。这仅适用于NATURAL LANGUAGE MODE选项。

不要挑剔，但它应该完美地运作，没有任何引号：

mysql> select * from table1;
+---------+------+------+-------------+
| autonum | ID   | name | metavalue   |
+---------+------+------+-------------+
|       1 |    1 | Rose | Drinker     |
|       2 |    1 | Rose | Nice Person |
|       3 |    1 | Rose | Runner      |
|       4 |    2 | Gary | Player      |
|       5 |    2 | Gary | Funny       |
|       6 |    2 | Gary | NULL        |
|       7 |    2 | Gary | Smelly      |
+---------+------+------+-------------+
7 rows in set (0.00 sec)

mysql> select ID, group_concat(coalesce(metavalue,'Empty')) as Test from table1 group by ID order by Test;
+------+----------------------------+
| ID   | Test                       |
+------+----------------------------+
|    1 | Drinker,Nice Person,Runner |
|    2 | Player,Funny,Empty,Smelly  |
+------+----------------------------+
2 rows in set (0.01 sec)

mysql> select ID, group_concat(coalesce(metavalue,'Empty')) as Test from table1 group by ID order by Test desc;
+------+----------------------------+
| ID   | Test                       |
+------+----------------------------+
|    2 | Player,Funny,Empty,Smelly  |
|    1 | Drinker,Nice Person,Runner |
+------+----------------------------+
2 rows in set (0.00 sec)

Server version: 5.5.24-0ubuntu0.12.04.1 (Ubuntu)

（这种查询在我的Windows 5.1.x安装工作中完全正常）

全文Sql查询

4 个答案: